The present invention pertains to medical imaging systems. More particularly, the present invention relates to a method and apparatus for generating images in a medical imaging system based on detected radiation by applying Compton scattering and deconvolution principles.
In nuclear medicine, images of internal structures or functions of a patient""s body are acquired by using one or more gamma camera detector heads to detect radiation emitted by a radiopharmaceutical that has been injected into the body. A computer system controls the gamma camera detector heads to acquire data and then processes the acquired data to generate images. Nuclear medicine imaging techniques include single photon emission computed tomography (SPECT) and positron emission tomography (PET). SPECT imaging is based on the detection of individual gamma rays emitted from the body, while PET imaging is based on the detection of gamma ray pairs resulting from electron-positron annihilations and emitted in coincidence with each other.
Existing gamma cameras commonly utilize a heavy lead collimator, a planar scintillation crystal, and a coarse array of bulky photomultiplier tubes (PMTs). The collimator absorbs all incident gamma photons except those traveling in a specific direction at each cell in the collimator in order to reconstruct a meaningful two-dimensional planar image. Collimators with different acceptance geometries are available, but must be physically exchanged with a cumbersome transport mechanism capable of supporting their substantial weight.
A collimator drastically reduces the counting efficiency of the gamma camera. It adds great weight to the camera detector heads which, in turn, must be supported by a very heavy gantry. Exchanging collimators requires time and labor, thereby reducing patient throughput. The bulky exchange mechanism occupies a sizeable space and is subject to mechanical misalignment, thereby requiring service calls.
PMTs are an old technology that has not fundamentally changed in decades. PMTs are not only bulky, but also consume energy, generate heat, and require replacement when their efficiency decays or when they fail.
The present invention includes a Compton deconvolution camera that comprises at least two detection layers, each to detect events resulting from incident photons. The camera further includes position sensing logic to determine positions of events in each of the detection layers, a coincidence detector to detect pairs of coincident events resulting from Compton scattering, and processing logic. For each of a plurality of subsets of one of the detection layers, the processing logic associates data representing detected events with a distribution of corresponding events in the other detection layer, based on the detected pairs of coincident events. The processing logic then uses a deconvolution function to localize probable source locations of incident photons, and then uses the probable source locations to reconstruct an image of an object.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.